1. Field of the Invention
This invention relates to the production of synthesis gas by the partial oxidation of hydrocarbonaceous materials. More particularly, this invention relates to controlling the pH of water used to quench and scrub raw synthesis gas.
2. Description of the Prior Art
The partial oxidation of hydrocarbonaceous materials to produce synthesis gas, a mixture of hydrogen and carbon monoxide, is well known in the art. A wide variety of carbon-containing materials have been employed as feed to partial oxidation processes including both solid carbonaceous fuels, such as coal, lignite, oil shale and tar sands, as well as liquid carbonaceous fuels, such as heavy fuel bottoms and residua. The carbonaceous fuel is introduced into the gas generator together with a free-oxygen containing gas to produce the mixture of raw synthesis gas which contains entrained solids, e.g., soot and ash, as well as quantities of other gases, which may include H.sub.2 O, CO.sub.2, H.sub.2 S, COS, CH.sub.4, NH.sub.3, N.sub.2 and Ar. The raw synthesis gas exits from the reaction zone at a temperature in the range of 1300.degree. to 3000.degree. F. The hot synthesis gas passes from the generator and is scrubbed and quenched with a water stream to remove soot and ash and cool the gas. The water stream, containing soot and ash, as well as some of the gases from the synthesis gas, is then mixed with naphtha and introduced into a decanter where two phases form. A soot-rich naphtha phase is removed from the decanter for further processing while an aqueous phase, commonly known as gray water, is removed for further processing. This aqueous phase contains dissolved salts, dissolved gases and ash while the organic phase consists of an organic extractant and the soot, i.e., particulate carbon. The use of a quench-scrubber and the two phase decanter is taught in U.S. Pat. Nos. 4,014,786 of Potter, et al. and 4,141,695 of Marion, et al. U.S. Pat. Nos. 4,141,695; 4,205,962 and 4,205,963, all of Marion, et al., 4,466,810 of Dille, et al. and 4,588,418 of Gabler, et al. all disclose the processing of the aqueous phase whereby it is sent to a flash column to remove gases, followed by settling to remove particulate matter therefrom with a subsequent recycle of the recovered water to the quench-scrubber. The organic extractant-soot phase may be treated to recover the extractant for reuse and to incorporate the particulate carbon into the hydrocarbonaceous material serving as feed to the synthesis gas generator as disclosed in Marion '695 and U.S. Pat. Nos. 4,211,638 of Akell, et al., 4,705,537 of Yaghmaie, et al. and the Dille and Gabler patents disclose the use of a hydrocyclone for the removal of particulate matter from the gray water. The use of surfactants to promote the separation of particulate matter is disclosed in Dille (cationic polyelectrolyte polymer) and Yaghmaie (anionic sulfonated product of humic acids or their salts). The process disclosed in Yaghmaie does not employ an inorganic extractant, but rather separates the particulate ash and dissolved materials without employing an organic extractant or the decanter employed in other prior art processes. Marion '695, '962 and '963, Dille and Gabler disclose the recycling of the water for reuse in the quench-scrubber after the water has been processed to remove significant quantities of particulate matter and dissolved gases.
U.S. Pat. No. 4,588,418 of Gabler, et al. discloses the use of water to remove ash and soot from the synthesis gas, the mixing of the water with an organic extractant, the separating of these two streams in a decanter to form an aqueous phase and an organic phase, the subsequent treatment of the aqueous phase in a flash separator to remove dissolved gases and the separation of the solids from the water bottoms of the flash separator in a hydrocyclone with a recycle of the remaining water to the quench scrubber.
A purge stream from the hydrocyclone which contains the solids from the water flash bottoms in concentrated form, is normally about 5 to 25% of the total water flash separator bottoms and is adjusted to keep the ash concentration at reasonable levels in the remaining water recycled to the synthesis gas quench system. Both acidic compounds, such as formic acid, as well as basic compounds, such as ammonia, are formed in the partial oxidation reaction and in the subsequent quenching process. The use of some hydrocarbonaceous feedstocks employed in the partial oxidation process result in an unacceptable acidic pH in the quench system, which in some prior art processes is alleviated by the injection of anhydrous ammonia or aqueous ammonia directly into the high pressure quench system or to the portion of the water flash separator bottoms stream that is recycled to the quench portion of the process. Additions of sodium hydroxide to raise the pH in this system is not appropriate, because the presence of sodium can cause additional ash formation resulting in unacceptable fouling of the processing equipment.
It is an object of this invention to provide effective control of pH in the water quench-scrubber system and in the subsequent water processing portion of a partial oxidation process.
It is a further object of this invention to utilize available streams having a basic pH for use in controlling the pH in the water-scrubber and attendant water processing equipment in a partial oxidation process.
It is a further object of this invention to process and recycle ammonia-bearing water as a means of controlling the pH in the water-quench scrubber and attendant waste processing equipment of a partial oxidation process.
The achievement of these and other objects will be apparent from the following description of the subject invention.